Stellar flybys like the one during which Proxima joined the
Alpha Cen system are extremely rare on human lifetimes, but
common by astronomical standards. Our Solar system underwent
one only about 70 thousands of years ago
[1]}, [2]}, [3]},
but the passing star had only \(\sim \) 15 % of the Solar mass
(Proxima is comparable – 12 % of the Solar mass). Such
events rise the question of the fragility of the planetary
systems [4]}. They are difficult to
detect, because the encounters are statistically likely to
involve the most common type of stars in the Milky way –
low-mass, cool and intrinsically faint objects – the reason
why Proxima itself was discovered only in 1915 by Robert
Innes [5]}, [6]} when
astronomical photography became a common tool, making it
possible to carry out studies of proper motions of thousands of
stars. The work of Innes was an early but important precursor
of moderns space missions like HIPPARCOS
[7]} and Gaia [8]}
that draw detailed maps of the Milky Way and its nearest
neighboring galaxies.
